1、Designation: A 428/A 428M 06Standard Test Method forWeight Mass of Coating on Aluminum-Coated Iron or SteelArticles1This standard is issued under the fixed designation A 428/A 428M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test method covers
3、procedures for determining theweight mass of coating on aluminum-coated iron or steelsheets and wire, and on other aluminum-coated iron and steelarticles.1.2 The final results determined by this test method shall beexpressed in inch-pound units or SI units, depending on theunits used in the material
4、 specification to which the results areto be compared. Certain portions of the procedure involvingdetermination of specimen weight mass have traditionallybeen performed in SI units, and corresponding inch-poundunits are not included.1.3 For sheet products, the final results are expressed aseither co
5、ating weight mass total both sides, or coating weightmass separately on each side, depending on the specifiedrequirements.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-
6、priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For a specificprecautionary statement, see Note 1.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterE29 Practice for Using Significant Digits in Test Data toDete
7、rmine Conformance with SpecificationsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Significance and Use3.1 This test method provides a standard method of deter-mining the weight mass of coating for comparison withspecification requirements. A coa
8、ting of aluminum on iron orsteel articles provides protection against corrosion by forminga relatively inert barrier. Specifications for aluminum-coatedarticles occasionally provide for different classes (weights)masses of coating so that the purchaser can select the coatingweight mass most suited t
9、o his needs. The heavier coatingwill provide greater protection against mechanical damagewhich may break the coating.4. Reagents4.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of
10、the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.3Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.4.2 Purity of
11、WaterWater used in preparation of reagentsolutions shall conform to Specification D 1193, Type IV orbetter.4.3 Antimony Trichloride SolutionDissolve 200 g of an-timony trichloride (SbCl3) in 1000 mL of concentrated hydro-chloric acid (HCl, sp gr 1.18 to 1.19) without heating.4.4 Hydrochloric Acid (s
12、p gr 1.18 to 1.19)Concentratedhydrochloric acid (HCl).1This test method is under the jurisdiction of ASTM Committee A05 onMetallic-Coated Iron and Steel Products and is the direct responsibility ofSubcommittee A05.07 on Methods of Testing.Current edition approved Nov. 1, 2006. Published December 200
13、6. Originallyapproved in 1958. Last previous edition approved in 2001 as A 428/A 428M - 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Su
14、mmary page onthe ASTM website.3Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., a
15、nd the United States Pharmacopeiaand National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,MD.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.5
16、Sodium Hydroxide Solution (20 %)Dissolve 20 partsby weight mass of sodium hydroxide (NaOH) in 80 parts ofwater.4.6 Stannous Chloride SolutionDissolve 100 g of stan-nous chloride (SnCl22H2O in 1000 mL of concentrated hydro-chloric acid (HCl, sp gr 1.18 to 1.19) without heating. Add afew granules of r
17、eagent grade tin.4.7 Hydrochloric Acid (1 +1)Mix 500 mL of HCl (sp. gr.1.18 to 1.19) with 500 mL of reagent water and cool to roomtemperature.NOTE 1Warning: Small amounts of the poisonous gas stibine (SbH3)may be evolved during the stripping process using the hydrochloricacid-antimony trichloride-st
18、annous chloride method. Hydrochloric acidfumes are present, and hydrogen gas is evolved in the stripping process.Therefore, the test should be performed under conditions of adequateventilation.Afume hood is recommended for large numbers of samples orwhere the test is to be carried out frequently ove
19、r extended periods oftime.5. Sampling5.1 Aluminum-Coated SheetsSamples for weight-of-coating mass-of-coating determination shall be secured asdesignated in the appropriate specification. Test specimensshall have a minimum area of 3 in.22000 mm2 of sheet, butpreferably approximately 5 in.23300 mm2 of
20、 sheet.NOTE 2For convenience in calculating test results in inch-poundunits, the specimen should have an area of 5.08 in.2of sheet (2.25 6 0.01in. square or 2.54 6 0.01 in. in diameter). The weight mass of coatingin grams on a specimen of that area is numerically equal to the weightmass of coating i
21、n ounces per square foot of sheet. For results to bereported in SI units, the specimen should have an area of 3330 mm2ofsheet (57.7 6 0.1 mm square or 65.1 6 0.1 mm in diameter).5.2 Aluminum-Coated WireSamples shall be secured asdesignated in the appropriate specification. The specimen ofaluminum-co
22、ated wire may be of any length over 12 in.(approximately 300 mm), but preferably about 24 in. (approxi-mately 600 mm). Where a continuous length is not available,shorter lengths totaling over 12 in., but preferably about 24 in.,shall be used. Since the density of the steel is known (0.283lb/in.3or 7
23、830 kg/m3), it is not necessary to use a specificlength of specimen.5.3 Aluminum-Coated Articles Other Than Sheet or WireSamples for weight mass of coating determination shall besecured as designated in the appropriate specification. Exceptas otherwise provided, the specimens should have a minimumar
24、ea of 3 in.21935 mm2 of aluminum-coated surface. For verysmall items, several pieces may have to be stripped to obtainthe minimum area.5.3.1 In the case of threaded articles, such as bolts andscrews, the determination shall be made on a portion of thearticle that does not include any thread.6. Proce
25、dure6.1 Strip the aluminum coating from the specimens by usingone of the following methods the sodium hydroxide-hydrochloric acid method (method A), the hydrochloric acid-antimony trichloride-stannous chloride method (method B) ordilute hydrochloric acid method (method C).NOTE 3Methods A and B are t
26、he most common methods used forsheets.6.2 Clean the specimens immediately before determiningthe weight mass by washing in petroleum ether or othersuitable solvent, and dry thoroughly.6.3 Determine the weight mass of the specimens individu-ally to the nearest 0.01 g.6.4 Sodium Hydroxide-Hydrochloric
27、Acid Method (methodA)Heat the NaOH solution to approximately 195F 90C(Note 4) and immerse each specimen in the hot solution untilthe strong reaction ceases. With silicon-free coatings, evolutionof gas for considerable time is likely, but do not leave thespecimens in the solution for more than a few
28、minutes. Longerimmersion inhibits the removal of coating during subsequentdips. Immersion of several specimens simultaneously is per-mitted provided all surfaces are freely exposed to the solution.Remove specimens from solution and scrub all surfaces underrunning tap water with a clean cellulose spo
29、nge to remove theloose deposit formed in the NaOH solution. Use vigorousscrubbing as necessary for some types of coating, but do notuse abrasive materials to remove the deposit. Blot with a towelto remove most of the water (Note 5) and immerse eachspecimen singly for not more than3sinHCl(spgr1.18 to
30、1.19) at room temperature. Remove, scrub again under runningtap water with a sponge, and re-immerse in the hot NaOHsolution for not more than a few minutes or until action againceases. Repeat this cycle until immersion in HCl shows novisible reaction (Note 6). Use one to three or more cycles asrequi
31、red, depending on the type and weight of coating. Afterthe final immersion in the NaOH and HCl solutions, scrub asbefore, dry thoroughly, and determine the weight mass ofeach specimen to the nearest 0.01 g.NOTE 4This temperature is not critical, but the solution should beheld several degrees below t
32、he boiling point (approximately 105C) toprevent excessive foaming during the first immersion. The beaker used forheating the solution and immersing the specimens should be less than halffull of solution to avoid the danger of foaming over when the specimensare immersed.NOTE 5Most of the water should
33、 be removed to prevent dilution ofthe HCl, as dilute HCl will attack the base metal to a greater extent thanconcentrated HCl.NOTE 6It is sometimes difficult to determine the point at which all ofthe alloy layer has been removed, when stripping silicon-free coatings. Ifin doubt, determine the weight
34、mass of the specimen (after scrubbingand drying) and then put it through one additional stripping cycle. Loss inweight mass due to the additional cycle will be of the order of 0.005 gon a 2.25-in. 57.2-mm square sheet specimen, if all the coating had beenremoved before the extra cycle.6.5 Hydrochlor
35、ic Acid-Antimony Trichloride-StannousChloride Method (method B)After determining the weightmass, immerse each specimen singly in a solution made bymixing 100 mL of antimony trichloride solution and 100 mL ofstannous chloride solution (Note 7). Allow the specimen toremain immersed until the evolution
36、 of hydrogen has ceased.Action will stop after 1 to 4 min, or somewhat longer,depending on the thickness and silicon content of the coating.Use fresh solution for each test (Note 8). The temperature ofthe stripping solution shall not exceed 100F 38C. Afterstripping, wash the specimen and scrub it wi
37、th a soft cloth,A 428/A 428M 062using a small amount of abrasive cleansing powder if neces-sary. Rinse the specimens and dry thoroughly with an absor-bent cloth or paper, and determine the weight mass of eachspecimen to the nearest 0.01 g.NOTE 7Mix the antimony trichloride and stannous chloride solu
38、tionstogether as needed.NOTE 8Very heavy coatings may show residual coating after allaction has stopped. If on examination after stripping, any coating stillremains, repeat the immersion step using fresh solution.6.6 Dilute Hydrochloric Acid Method (1 + 1) (methodC)After determining the weight (mass
39、), immerse each speci-men singly in the stripping solution and allow to remain untilthe violent evolution of hydrogen has ceased and only a fewbubbles are being evolved. Action will stop after 1 to 4 min orsomewhat longer depending on the thickness and siliconcontent of the coating. Use of the same
40、solution is permitteduntil the time for stripping becomes inconveniently long. Thetemperature of the stripping solution shall at no time exceed100F 38C. After stripping, wash the specimens by scrub-bing them under running water, dip in hot water and wipe orblow dry. Determine the weight mass of each
41、 specimen to thenearest 0.01 g.6.7 Sheet SpecimensWhen measuring the total coatingweight mass on both sides, or the single side coating weightmass on each side, determine the area of sheet (one surface)to the nearest 0.01 in.25 mm2. If specimens were prepared tothe dimensions as provided in Note 2,
42、they shall be presumedto have an area of 5.08 in.23330 mm2. When it is not possibleto determine the area accurately, as in specimens from corru-gated sheets, determine the average thickness of the strippedsheets to the nearest 0.001 in. 0.01 mm.6.7.1 When determining the single side coating weightma
43、ss of sheet material, use the procedures described in 6.4,6.5,or6.6, except use a “stop-off” to protect the second sidefrom the stripping medium. Acid-resistant paints or lacquers,acid-resistant tape, or mechanical devices fastened to the testspecimen are examples of commonly used “stop-off” materia
44、ls.Apply the “stop-off” to the specimen after the first determina-tion of weight mass and remove before the second determi-nation of weight mass. Because of the possibility of moistureabsorption during the stripping process, the “stop-off” must notbe on the specimen during either weight mass determi
45、nations.Determine the coating weight mass on the second sidesubsequently without a “stop-off” on the first side.6.8 Wire SpecimensDetermine the diameter of thestripped wire to the nearest 0.001 in. 0.01 mm by taking theaverage of two measurements at right angles to each other.6.9 Specimens Other Tha
46、n Sheet or WireDetermine thetotal coated area of the original specimen to the nearest 0.01in.25 mm2. Alternatively, for specimens of uniform thicknessof base metal, such as a piece of plate or pipe, determine theaverage thickness of the stripped specimen to the nearest 0.001in. 0.01 mm.7. Calculatio
47、n7.1 Aluminum-Coated Sheet:7.1.1 Results in Inch-Pound Units:7.1.1.1 When the area of one surface of the sheet isdetermined, calculate the weight mass of aluminum coatingas follows:C 5 W12 W2!/A 3 K (1)where:C = weight mass of coating, oz/ft2of sheet,W1= original weight mass of specimen, g,W2= weigh
48、t mass of stripped specimen, g,A = area of one surface of the sheet, in.2or mm2, andK = a constant = 5.08 when A is in in.2, or = 3.28 3 103when A is in mm2.NOTE 9If the specimen was prepared to the dimensions as provided inNote 2, having an area of 5.08 in.2, the loss of weight mass in grams isnume
49、rically equal to the weight mass of coating in ounces per squarefoot of sheet.7.1.1.2 When it is not possible to secure a specimen ofmeasurable area, calculate the weight mass of coating asfollows:C 5 W12 W2!/W2# 3 T 3 K (2)where:C = weight mass of coating, oz/ft2of sheet,W1= original weight mass of specimen, g,W2= weight mass of stripped specimen, g,T = thickness of stripped sheet, in. or mm, andK = a constant = 652 when T is in in., or = 25.7 wh
